Find two positive numbers `x` and `y` such that `x+y=60` and `x y^3` is maximum.

Explanation

To find two positive numbers \( x \) and \( y \) such that \( x + y = 60 \) and \( xy^3 \) is maximized, we can follow these steps:

### Step 1: Express one variable in terms of the other
Given the constraint \( x + y = 60 \), we can express \( x \) in terms of \( y \):
\[ x = 60 - y \]

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